No description available.

No description available.

The Dos Cabezas Mountains lie in the northeastern most part of Arizona, in Cochise county. They area medium-sized range of some 150 square miles area, and are almost wholly surrounded by unconsolidated basin-fill material. Most of the range is composed of a number of Precambrian igneous and metamorphic rock masses. Its core is composed of a large, complex, terrain of Cretaceous intrusive volcanic breccias and magmatic aphanites. A large number of Laramide and mid-Tertiary intrusive plutons and dikes cut the range. The Precambrian rocks consist of eight granitoid plutons and three areas of phyllitic and argillitic metamorphosed sediments and volcanics. The metamorphic rocks display a primary greenschist facies dynamothermal metamorphic fabric and a later superimposed biotite-forming hornfelsic thermal metamorphic fabric. The metasediments are mostly phyllites and argillites, but contain over 10,000 feet of metaconglomerate showing marked primary cross-bedding. Many of the metamorphic units are weakly metamorphosed volcanic flows or tuff-contaminated fluvial clastic sediments. These rocks are all classified as Pinal Schist, although some may be equivalent Mazatzal Quartzite. The plutons consist of a pre-Pinal-metamorphism dacite porphyry stock, one quartz monzonite gneiss synkinematic with the Pinal dynamothermal metamorphism, and four gneissic quartz monzonite plutons which appear to post-date the Pinal metamorphism and imply a mild tectonic event at about 1450 million years ago, and two large post-kinematic quartz monzonite stocks which are of circa 1400 million years age. One of these latter stocks displays prominent rapakivi texture; this is considered to be the result of normal magmatic crystallization. The texture is caused by reaction breakdown of hornblende to form biotite among crystals floating in the magma, thereby extracting potassium from the magma and temporarily halting potash feldspar crystallization while allowing plagioclase crystallization. Rb-Sr dating of the plutons reveals that one of the older post-Pinal gneisses is 1470 ± 30 m.y. old, while the rapakivi is 1380 ± 30 m.y. old and the other large stock is 1425 m.y. old and has undergone a marked Sr redistribution at 1000 m.y., ago; this thermal event has biased all the Precambrian K-Ar ages in the northwestern part of the range toward 1000 m.y., also. A large complex assemblage of Cretaceous welded intrusive volcanic breccias underlies 17 square miles of the core of the range. They are largely composed of small angular fragments torn from foundering large fragments of surficial andesite flows, sinking in a fluidized bed. The gas source was a crystallizing magma at depth; entrained quartz and plagioclase crystals from this magma appear in the breccia ground mass. The breccias are cut by a large number of small mafic magmatic instrusives. Several large diabasic and quartz dioritic plutons of Cretaceous or Paleocene age appear in the range and mark Laramide plutonism. K-Ar data from all but the northwestern most part of the Precambrian rocks in the range display a remarkably uniform Paleocene age which reflects a Paleocene thermal metamorphism. Mid-Tertiary plutonism is recorded by several mafic dike sets, including one of "Turkey Track" andesite porphyry, a granodiorite stock, and numerous quartz veins. Basin and Range block faulting is not obvious in the range, but may account for its present high-standing nature, especially along the northern range margin. Dynamothermal metamorphism is recorded strongly in the Pinal Schist, and dynamic tectonism, at circa 1450 million years. Thermal metamorphism is recorded at 1000 million years, circa 55 million years, and circa 35 million years. Plutonism is recorded before Pinal metamorphism, during Pinal metamorphism, then over the 1470-1380 million year interval, in the Cretaceous-Paleocene Laramide interval, and in the mid-Tertiary Oligocene-Miocene interval.

No description available.

No description available.

No description available.

The recreational use of the Colorado River within the Grand Canyon National Park and National Monument increased on the order of 60 to 70 per cent during each year of the interval 1967 to 1970. Consequently, the U. S. National Park Service instituted user limits to protect and preserve the area commencing with the 1971 season. This limit was established with limited data on the users of the river or about their perceptions of the trip experience. A need existed to collect and analyze this type of data, and to suggest possible management alternatives. This study used a mailed questionnaire to a random sample of past participants in order to collect basic socio-economic data. The analysis was based on a 65% response rate, and consisted of individual question tabulation and multivariate data -cluster analysis. The data show background characteristics of the participants, reasons for taking the trip, reactions to the experience, perceptions of problems associated with the trips, reactions to crowded conditions, and needs for regulatory policy concerning user intensities.

Design of engineering projects involve a certain amount of uncertainty. How should design decisions be taken in face of the uncertainty? What is the most efficient way of handling the data? Decision theory can provide useful answers to these questions. The literature review shows that decision theory is a fairly well developed decision method, with almost no application in hydrology. The steps of decision theoretic analysis are given. They are augmented by the concept of expected expected opportunity loss, which is developed as a means of measuring the expected value of additional data before they are received. The method is applied to the design of bridge piers and flood levees for Rillito Creek, Pima County, Arizona. Uncertainty in both the mean and the variance of the logarithms of the peak flows of Rillito Creek is taken into account. Also shown are decision theoretic methods for: 1) handling secondary data, such as obtained from a regression relation, 2) evaluating the effect of the use of non - sufficient statistics, 3) considering alternate models and 4) regionalizing data.It is concluded that decision theory provides a rational structure for making design decisions and for the associated data collection and handling problems.

No description available.

The Swisshelm Quartz Monsonite covers about two square miles on the western slope of the Swisshelm Mountains, Cochise County, Arizona. Field observation and petrographic study indicate that the quartz monsonite was derived by differentiation and late-stage alkali metasomation of probably a quartz dioritic magma rich in alkali and volatile constituents. The high concentration of the volatiles is believed to be of great importance in the development of the different facies and rock types. Four different facies of the Swisshelm Quartz Monsonite have been distinguished as (1) the normal facies, (2) the altered facies, (3) the fine-grained facies, and (4) the contact facies. Also, several aplite dikes, local beryl-bearing pegmatite patches, and numerous quartz veins are present and attributed to late magmatic differentiation. Inclusions of an early and late magmatic facies are sparcely disseminated through the quartz monsonite. The Swisshelm Quartz Monsonite magma has intruded and metamorphosed the Upper Paleozoic sediments of the Mace Group as well as the Lower Cretaceous sediments of the Bisbee Group. The metamorphism is of a contact metasomatic type to which the mineralogical and textural changes in the country rocks have been attributed.